This invention relates to a connecting device for connecting chromatographic separating columns of glass to terminal fittings on a chromatographic apparatus.
The published German specification 2,029,738 shows a connection fitting for a laboratory apparatus of glass having a connection socket which is provided with grooves to retain a hose pushed thereon. A threaded bushing is slid on the connection socket and a sealing ring of rubber-like resilient material, such as a piece of rubber hose, is pushed on the connection socket, the sealing ring being deformed thereby to closely engage the connection socket and also to fill the grooves therein. The connection fitting slid thereon is threaded with an internal thread on the external thread of the threaded bushing, and the sealing ring is deformed between the connection fitting and the threaded bushing by tightening the thread and is tensioned against the connection socket. The bore of the connection fitting has an inclined shoulder, and, correspondingly, the bore of the threaded bushing has a flaring inclined shoulder at its end facing the sealing ring. A connection fitting of the type having a sealing ring of rubber-like material is neither intended nor suitable for use at high temperatures, such as 350.degree. C., occurring in gas-chromatographic separating columns, as the material of the sealing ring is not able to withstand these temperatures.
Swiss patent 509,591 shows a closure device for a chromatographic tube in which two sealing rings of rubber-like material are interposed between a plug or core member and the internal wall of the chromatographic tube and a spacer tube is arranged between these sealing rings. The sealing rings have trapeziodal cross sections flaring outwardly, whereby they can be pressed by axial pressure against the internal wall of the tube. This axial pressure is exerted by the annular part of a thrust member the conical end face of which engages a conical end face of one sealing ring. A conical surface of a flange provided on the plug engages a conical end face of the other sealing ring. The thrust member is axially adjustable relative to the core member. As in the case of the aforementioned German specification, this closure device is neither intended nor suitable for use at high temperatures because of the material of the sealing ring.
There are various other connecting devices for gas-tight sealing connection of the ends of separating columns to terminal fittings on the chromatographic apparatus. These are the conventional means for detachably and sealingly connecting tubes, such means comprising conical sealing end faces which are tightened by means of a screw cap. Using such connecting devices with chromatographic columns made of glass encounters problems in practice. The presently available detachable connecting devices for chromatographic separating columns made of glass are adapted for use at temperatures up to 230.degree. C. They may be used for a short time and without rapid temperature variations up to temperatures of 300.degree. C. In recent times, however, gas-chromatography requires glass column connections which remain gas-tight even, if a temperature program up to about 350.degree. C. is used, and which are still easily detachable. It is to be noted that gas-chromatography requires frequent interchanging of the separating columns and thus a correspondingly frequent detaching of the connections. The prior art glass column connections are not adapted to meet these requirements.
It is an object of the invention to provide a connecting device for connecting chromatographic columns of glass to the terminal fittings on the apparatus, said connecting device being easily detachable, gas-tight up to 350.degree. C. and indifferent to thermal shocks.
According to the invention, there is a connecting device for connecting chromatographic separating columns of glass comprising connecting means for effecting gas-tight and detachable connection of the ends of the separating column to terminal fittings on a chromatographic apparatus. The ends of the column of glass are surrounded by a metallic sleeve, a sleeve of synthetic plastic having at least one conical end face being interposed therebetween. The synthetic plastic sleeve is held in sealing engagement with the separating column, on one hand, and with the metal sleeve, on the other hand, by a sleeve-shaped thrust member, which is axially adjustable relative to the metallic sleeve. A radial sealing force is exerted on the synthetic plastic sleeve through its conical end face by an abutting complementary conical surface. The connecting means are provided on the metal sleeve.
According to one aspect of the invention the synthetic plastic sleeve consists of a synthetic plastic material which is of substantially stable shape at least up to a temperature of 350.degree. C. even if subjected to pressure.
The invention is based on the discovery that a sufficient radial sealing force can be achieved by the wedge effect through the conical end faces even with a synthetic plastic material which has no rubber-like characteristics but is of substantially stable shape. Thus a temperature resistant synthetic plastic material such as polyimide can be used and, thereby, such a connecting device is adapted to be used for connecting chromatographic separating columns which are subjected to a temperature program up to 350.degree. C.
There are materials which, though they are of substantially stable shape and have no rubber-like characteristics, tend to flow under the influence of the pressure and of high temperature or are subject to material losses due to evaporation, whereby the axial pressure exerted by the thrust member and causing the sealing force relaxes and the seal becomes leaky. A material of this type is, for example, polytetrafluoroethylene. Due to its other especially advantageous characteristics this type of material cannot always be replaced by other materials.
It is a further object of the invention, to provide a connecting device of the type mentioned hereinbefore in which the sealing synthetic plastic sleeve may be made of a material having a tendency to flow or vaporize under the influence of pressure and temperature, and which, nevertheless, remains gas-tight and permits repeated use of any particular sealing plastic sleeve.
It is a more specific object of the invention to provide a connecting device of the type described hereinbefore, in which the sealing synthetic plastic sleeve is made of polytetrafluoroethylene.
According to another aspect of the invention the plastic sleeve is held at an adjustable minimum axial pressure in sealing engagement with the metal sleeve and the separating column. For this purpose one end face of a sleeve-shaped thrust member engages the adjacent end face of the synthetic plastic sleeve, and a spring compressible by means of an axial adjusting device abuts the other end face of the thrust member.